These days, there are many IoT (Internet of Things) products on the market, such as human body surface temperature and humidity sensors, 3 g gravity sensors, and other devices for urine detection, motion mass detection, and so on. However, most of these sensors have the common feature that they are small in size and that they must be closely attached to the clothing on the human body when in use. Conventional retaining devices are unable to retain these small-sized detective sensors, so that the accuracy and reliability of the collected data is poor. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.